In recent years, a displacement controlling element which permits adjusting the length of a optical path and the spatial position in the order of a sub micron is required in the field of the optics, precision machining engineering, semiconductor manufacturing engineering and so on. For this purpose, a piezoelectric/electrostrictive actuator, which utilizes a strain resulting from the reverse piezoelectric effect or the electrostrictive effect induced by applying an electric field to a ferroelectric material or an antiferroelectric material, has been developed. Compared with the conventional electromagnetic elements, such as servomotors, pulse motors, and so on, such a displacement control element with the aid of the strain induced by the applied electric field has characteristic features such that the micro displacement can be easily attained, and a high efficiency in converting the electric energy to the mechanical energy or vice versa provides a reduction in the consumption of an electric power. Furthermore, an extremely high precision in assembling the components of the displacement control element provides small and lightweight products. Thus, it is considered that the applicable field thereof will increase continuously.
In an optical switch, for instance, such a piezoelectric/electrostrictive element is normally used to switch transmission channels for an incident light. An example of such an optical switch is shown in FIGS. 2(a) and (b). The optical switch 200 shown in FIGS. 2(a) and (b) comprises a light transmitting member 201, a light path changing member 208 and an actuator member 211. In a more detailed description, the light transmitting member 201 includes a light reflecting plane 101 disposed in a part of a surface facing the light path changing member 208, and light transmitting channels 202, 204 and 205 directed in three different directions from the light reflecting plane 101, and the light path changing member 208 includes a transparent light incident member 209 movably disposed in the vicinity of the light reflecting plane 101 in the light transmitting member 201 and a light reflecting element 210 for providing a total reflection. Moreover, the actuator member 211 has a mechanism, which is displaced by an applied external signal and then transmits the displacement to the light path changing member 208.
In the optical switch 200, the actuator member 211 is activated by an external signal, e.g., an applied voltage, as shown in FIG. 2(a), and then the light path changing member 208 separates from the light transmitting member 201 by the displacement of the actuator member 211, so that light 221 incident in the light transmitting channel 202 of the light transmitting member 201 is reflected in the total reflection at the light reflecting plane 101 in the light transmitting member 201 without any transmission thereof, and is transferred to one of the light transmitting channels 204 on the exit side.
On the other hand, if the actuator member 211 is changed into the non-acting state from this state, the position of the actuator member 211 is turned to the initial position, as shown in FIG. 2(b), and the light incident member 209 in the light path changing member 208 comes into contact with the light transmitting member 201 within the distance less than the wavelength of light, so that the light 221 incident to the light transmitting channel 202 is transmitted from the light transmitting member 201 to the light incident member 209 with the action thereof, and then passes through the light incident member 209. The light 221 passed through the light incident member 209 arrives at the light reflecting element 210, and is transmitted to another light transmitting channel 205 on the exit side on which the light reflected by the light reflecting surface 101 of the light transmitting member 201 proceeds owing to the reflection by the light reflecting surface 102 of this light reflecting member 209.
As the actuator member of an optical switch having such a light path changing function, a piezoelectric/electrostrictive element is preferably used. In particular, in the design of a matrix type switch for switching between several channels, a piezoelectric/electrostrictive actuator including a plurality of piezoelectric/electrostrictive elements of a unimorph or bimorph type (hereafter, being referred to as bending displacement elements) is preferably employed, as disclosed in Japanese Patent No. 2693291 specification. The bending displacement element is constituted by a vibrating plate and piezoelectric/electrostrictive elements, and can provide a greater displacement, in proportion with the length of the piezoelectric/electrostrictive elements, since a slight expansive/contractive strain of the piezoelectric/electrostrictive elements induced by an applied electric field is converted into a bending displacement in the bending mode. However, since the strain was converted in such a way, the stress arising directly from the strain of the piezoelectric/electrostrictive elements could not be directly used, and therefore it was very difficult to increase the magnitude of the generated stress. Moreover, it was also difficult to increase the responsive speed satisfactorily, since the resonance frequency inevitably decreased with the increase of the length of the elements.
Meanwhile, in attaining an enhancement in the performance of an optical switch 200, firstly there is a requirement of increasing the ON/Off ratio (contrast). In this case, it is important to reliably perform the contact/separate action between the light path changing member 208 and the light transmitting member 201, and therefore the actuator member preferably provides a greater stroke, i.e., a greater displacement. Secondly, there is a requirement of reducing the power loss due to the switching. In this case, it is important to increase the area of the light path changing member 208 together with the increase in the effective area of the light transmitting member 201 coming into contact therewith. Since, however, such an increase in the contact area causes a reduction in the reliability of separation, an actuator generating a greater force is necessary. Hence, in enhancing the performance of such an optical switch, it is desirable to provide a piezoelectric/electrostrictive actuator including an actuator generating a greater displacement together with a greater force.
It is preferable that the individual piezoelectric/electrostrictive elements are constituted so as to be independent of each other. The independency mentioned herein implies that the generated displacement and the stress resulting therefrom in the respective elements do not interfere with each other, i.e., constrain each other in these elements. For instance, the piezoelectric/electrostrictive actuator 145 shown in FIG. 3 provides a bending displacement due to the activation of piezoelectric/electrostrictive elements 178, as shown in the sectional view of FIG. 4. Each piezoelectric/electrostrictive element 178 is mechanically independent of the adjacent piezoelectric/electrostrictive element with the aid of the rigidity of partition walls 143. However, a substrate 144 is formed in a unified element, and vibrating plates to which the piezoelectric/electrostrictive elements 178 act are also a continuous element. Accordingly, although the respective adjacent piezoelectric/electrostrictive elements are independent of each other by the partition walls 143, a tensile or compressive stress resulting from the action of the piezoelectric/electrostrictive elements 178 provides a certain influence between the piezoelectric/electrostrictive elements. On the other hand, in the piezoelectric/electrostrictive elements 155 shown in the sectional view of FIG. 5, a side walls 219 carrying a vibrating plates 218 is separated from the adjacent side walls 219, thereby providing no interaction with the adjacent elements.
Moreover, as another embodiment, actuators used for an ink jet head, which are disposed in a straight line in conjunction with pressurizing chambers disposed in a straight line, are disclosed in FIG. 2 of JP-A-60-90770. The actuators are formed not by the above-mentioned bending displacement elements, but by piezoelectric/electrostrictive elements, which directly utilize the strain of the piezoelectric/electrostrictive elements. In the actuators, however, electrodes are formed on the upper and lower activation surfaces of the piezoelectric/electrostrictive elements, and in general the piezoelectric constant d33 representing the longitudinal effect of the electric field induced strain is greater than the piezoelectric constant d31 representing the transversal effect of the electric field induced strain. Nevertheless, it was difficult to obtain a greater amount of displacement with a smaller applied voltage, since the distance between the electrodes is large. On the other hand, an actuator used by applying a voltage to the piezoelectric plate in the direction of the thickness thereof is disclosed in FIG. 5 thereof. In this actuator, there is used singly a single piezoelectric element produced by forming merely electrodes on a piezoelectric plate. Moreover, the piezoelectric element disclosed in JP-A-60-90770 is produced by processing the resultant with cutting using diamond saw, and therefore there is a problem in that the element is not free from damages inherently formed by the machining.
In any way, there has been so far no proposal of providing such a piezoelectric/electrostrictive actuator that piezoelectric/electrostrictive elements having little damage suffered in the manufacturing with both a greater displacement and a high generating force are arranged in the form of a two dimensional matrix, and are unified with the substrate into one body as well.